Method of and means for compressing gases



P 1933- B. 's'. AIKMAN v 1,927,864

METHOD OF AND MEANS FOR COMPRESSING GASES Filed April 11, 1930 4 Sheets-Sheet 1 Sept. 26, 1933. B. s. AIKMAN 1,927,854

METHOD OF AND MEANS FOR COMPRESSING GA$ES 7 Filed April 11, 1930 4 Sheets-Sheet 2 Sept. 26, 1933. B. -S. AIKMAN 1,927,864 I METHOD OF ANDJIEANS FOR COIIBRESSING GASES I Filed April 11,- 1930 4 Sheets-Sheet -3 A a I I Sept 26, 1933. Bj. s. AIKMAN 1,927,864

. METHOD OF AND IEANS FQRCOHPRESSING GASES lfiled April 11, 1930- "-{Sheets-Sheet 4.

Patented Sept. 26, 1933 UNITED STATES PATENT OFFIC METHOD OF AND MEANS FOR COMPRESS- I NG cases Burton S. Aikman, Milwaukee, Wis., assignor to National Brake & Electric 00., Milwaukee, Wis., a corporation of Wisconsin The present invention relates'to a method of and means for compressing gases. specific construction-which I shall describe herein as an embodiment of the invention is an air compressor, it is to be understood that the gas to be compressed is of no distinction, and it is further to be understood that certain features of the invention are applicable to pumps, engines, and like'related displacement apparatus. To meet the problem of a demand for compressors operating at high crank shaft speeds I have, heretofore, developed the ring friction actuated sleeve valve compressor-see my Patent No.'1,632,262. I have also developed methods of cooling compressorssee Patents 1,635,- 5241,699,941 and1,714,836. These developments have successfully met all the ordinary requirements of stationary types of. compressors, permitting them to be driven directly by electric motors of standard designs.

More recently, however, the problem of providing a compressor for automotive vehicle brakes has becomeacute.

It is desirable to drive the compressor directly from the engine because of the considerations of cost, of economy and of minimum weight. But known types of compressors are unable to stand up to these requirements because of the wide range of speeds under which such a device must be operated.

For example, consider a bus or the like, operating partly in a metropolitan area, involving low speed operation and also frequent gear changes, and also operating partly in a sparsely settled area, where high speed and continuous travel for relatively long periods is possible. It will be seen that the requirements are highly conflicting. In a metropolitan district the use of the brakes is frequent, calling for maximum delivery of the compressor. Hence, the compressor which is to be driven directly from the engine may be required to deliver the maximum output of air for frequent operation of the brakes while operating at relatively low speed, while at the same time it may be subjected momentarily to extremely high speeds in second gear, where rapid acceleration is required. In open road driving at high speed, where the brakes are used very little, the compressor may be called upon to operate continuously at high speed, and it must not overheat.

The two chief unfavorable factors for high speed operation of a compressor are, first, the difficulty of avoiding excessive heating, and sec- While the 0nd, the dimculty of securing adequate valve action.

In compressors of previously known design, excluding for the time my own prior developments in the sleeve valve compressors and the 0 schemes for cooling the same, the nearest approach to a vehicle type of compressor is one in which the valves are mechanically actuated, as by a common rotating valve for two cylinders.

In that compressor, however, the excessive 6 temperature rise is a fatal defect. This is due to a number of causes, one of which is the friction of themechanically actuated valve itself, and the difiiculty of lubricating it. Another is the unavoidable loss in volumetric efiiciency due 7 to the clearance required for that type of valve. In addition there is the problem of lubrication of both the valve and the compressor piston, which has been an extremely delicate problem. On the one hand, if ample lubrication is provided, the compressor will pass oil and'the same passes over into the discharge chamber and becomes carbonized, fouling the discharge check valve and valve seat and causing leakage of the same and breakage of the discharge check valve. D

On the other hand, if the lubrication is not ample, heating, due to friction, results, with consequent danger of destruction of the compressor.

The compressor of my invention, while it is designed primarily for vehicle brake operation and is adequate to meet the problem, is not to be limited to that particular type of work, but it will at once be appreciated by those skilled in the art that being capable of meeting such severe requirements it is capable also of meeting general requirements.

One of the distinctive features of the present invention is the high speed at which the compressor is capable of operation. The compressor of my invention is, in the preferred form, connected to the generator shaft of the engine, v which operates at twice the crank shaft speed of the engine. This means that the average driving speed at which the compressor operates is between 1600 and 1700 R. P. M. However, in second gear, the speed will be carried as high as 3750 R. P. M., and the compressor must be capable of operation under those conditions for as long periods as the engine is capable of operation in second gear.

I have operated a compressor of the type herein disclosed continuously for thirty eight hours, at a speed of 3450 R. P. M., without exceeding the permissible rise in temperature, with nothing more than a water hopper as the cooling means.

2 The compressor may be driven at a speed of 5000 R. P. M., intermittently, without injury.

In the normal installation of my compressor on an internal combustion engine driving a bus, truck or the like, a water jacket for the compressor cylinder is provided and this is connected into the water jacket and radiator cooling system of the engine. The high speed which this compressor will withstand is due to a number of contributing improvements which will be more fully appreciated from a specific description of an actual embodiment, but which may be briefly re- I ferred to herein as involving a new valve con- --small compressor of two-inch bore by one-inoh stroke, normally'displacing at 1600 to 1700 R. P. M. about 3.13 cubic feet of free air per minute and substantially twice that at double the aforesaid speed, and I find that for a receiver pressure of '75 pounds the volumetric efiiciency of the compressor is 78.6 percent. At one hundred pounds receiver pressure the volumetric efficiency was 68.5 percent and at one hundred and fifty pounds receiver pressure the volumetric efficiency was 59.4 percent. To one skilled in the art these figures, for so small a compressor and operating at such a high speed, appear to be amazingly high.

A number of factors contribute to this high eiiiciency, among them being the intake valve construction, which is simple, of exceeding rapidity of operation, providing a large inlet opening, with rapid opening and closing to the full extent in a minute fraction of the cycle of operation. Another feature is the unusually small clearance space and the extremely short passage between the valve and the interior of the cylinder. Another feature is the character of the lubricating system, no appreciable oil being passed by the piston and hence, fouling of the discharge valve being prevented, with consequent minimum leakage of the discharge check valve. Due to non-interference of the lubrication requirements with the valve action, the valvesthat is, both .the intake and the discharge valves-stay tight, and the aforesaid high efficiency may be maintained over long periods of use.

Due to the design of the compressor it is possible to operate the compressor at higher permissible temperatures without carbonization of oil or seizing of the piston than any compressor with which I am familiar. However, the compressor, due to its novel construction, operates at an unusually low temperature,considering the speed and the service which it performs so that for all normal requirements, air cooling alone is suflicient.

The compressor of my invention provides unusually large displacement, or capacity. When the .splacement is compared with other compressors on the basis of pounds of material, the ;-:-2parison is very greatly in favor of my compressor. The reasons for the high displacement are apparent from the foregoing, being due, first, to the high speed at which the device will operate satisfactorily, and the high pressures against which it will compress air, and second, to the high volumetric efllciency of which it is capable.

The compressor of my invention is compact and light in weight. It can be employed in situations where compressors of known types would be highly objectionable because of space requirements and weight. This applies particularly to vehicle construction, although there are numerous other applications where my compressor provides a unique solution. For example, on aeroplanes, airships and the like.

The compressor of my invention is well lubricated. The system of lubrication which I provide is exceedingly simple and provides automatically for ample lubrication of all parts requiring the same, but at the same time it prevents the passing of oil past the compressor piston or working head. The guiding part of the piston and its guide, together with the crank shaft and connecting rod bearing are splash lubricated, whereas the working cylinder is lubricated by a wiper which runs across or between the guiding cylinder and the working cylinder. All it does is provide enough lubrication for the ring valve, inasmuch as there is no appreciable bearing between the working piston head and the working cylinder.

'The compressor of my invention is easy to build and is of simple construction. While the results attained by the compressor of my invention are far in advance of previous types of compressors, these improved results are not dependent upon improvements in workmanship, but are dependent upon inventive concepts in the design of the compressor. The structure is simple, and easily manufactured according to known manufacturing methods, the parts being easily assembled and readily accessible for repairs or services.

There are a number of specific features of novelty in the structure to which attention will be more fully called later, but some of which may be referred to herein generally, namely,

First: The double use of the piston ring;

Second: The double use of the ring groove clearance;

Third: The double use of the piston skirt clearance;

Fourth: The lightness of the valve, together with its small throw, low inertia and relatively small degree of valve movement;

Fifth: The thermal separation of the two parts of the piston;

Sixth: The separation of the lubricating function into two parts having 'difl'erent requirements;

Seventh: The novel cooling of the working piston or piston head through free access of air which comprises 'mally closed by a pipe plug '7 or the like.

features which I have above enumerated I consider to be broadly new and intend to claim describe, in connection with the accompanying drawings, a specific embodiment of the same.

In the accompanying drawings, in which like reference numerals refer to like parts throughout:

Figure 1 is a vertical longitudinal section through a compressor of my invention;

Figure 2is a cross-section, taken on the line 22 of Figure 1;

Figure 3 is a cross-section, taken on the line 3-3 of Figure 1;

Figure 4 is a fragmentary sectional view illustrating the position of the ring valve during the compression stroke or" the piston;

Figure 5 is a similar fragmentary sectional view showing the position of the ring valve on the suction stroke of the piston;

Figure 6 is a vertical longitudinal section through a compressor of my invention, in which a receiver is mounted directly upon the working cylinder;

Figure '7 is a similar section of a modified form showing the use of a cooling water jacket;

Figure 8 is a transverse sectional view taken on the line 8'-8 of Figure 7;

Figure 9 is a fragmentary sectional view illustrating a modified form of intake valve;

Figure 10 is a similar fragmentary sectional view of a further modification;

Figures 11, 12 and 13 are similar views of modifications Figure 14 is a side elevation of the compressor shown in Figural; a1"

Figure 15 is a plan Referring first to main frame of th case and cylinder I of the same.

es 1 to 5 inclusive, the vine comprises a crank r; 1, the upper end of gral cylinder section 2 which comprises a crankand the lower case section 3, integral with the cylinder 2 and having at its base a suitable oil sump 4, formed in an enlargement of the lower end of the crank case. A lateral extension 5 of the sump is provided with a suitable draining opening 6, nor- A filling opening 8 for lubricant is provided in the top of the lateral extension 5 and this opening 8 is normally closed by a screw plug 9. The top of the opening 8 provides a suitable overflow for determining the level of oil in the bottom of the crankcase. This level is indicated by the line 10. The base 3 thus provides a relatively large volum'e of lubricating oil for operation of the com-' pressor over extended periods of time. The oil is preferably changed when the engine oil is changed.

The case 3 is provided on one or both sides with a suitable handhole 12 covered by a plate or cover member 13, this plate or cover member being removable for inspection of the lower end of the connecting rod 14 and its bearing upon the crank pin 15. The crank shaft 16, which is adapted to be driven by being coupled preferably to the pump or generator shaft of the engine'is mounted as shown in bearings of the roller type 17 and 18, "having their inner races mounted upon the ends of the crank shaft 16 and their suitable flanges upon the ends of the crankcase section 3. The end plates 19 and 20 are suitably piloted into cylindrical bores in the end walls of the chamber 3 and are located angularly by means of dowel pins 22 and 23. Suitable packing, such as 24, is clampedbetween the plate and the crankcasing to provide a tight joint. Gap screws such as 25 extend through the flanges of the end plates and are threaded into the metal ofthe case 3 surrounding the cylindrical bores in the end walls. The cover plate 19 is provided with a pocket 26 for a suitable packing or other sealing means for closing off the crank case and for preventing the escape of oil along the shaft 16. The

' cover plate 20 is imperforate and hence needs no shaft packing. Obviously, any suitable means weight of the connecting rod and the connected outer races mounted in'circular end plates 19' piston. These parts are made as light as is consistent' with the necessary strength and wearingfrom to the back of the roller bearings 1'7 and 18 for distributing lubricant thereto. The lubricant then drains back into the sump 4. The connecting rod cap 32 is provided with a dipper, or oil thrower 33 for causing oil to be carried upwardly to lubricate the crankshaft bearing, the connecting rod bearing and the piston with its guiding cylinder. The connecting rod is provided with lubricating passageways 3434, to provide suitable lubrication for the connecting rod 14 and crank 15.

A suitable liner of bearing metal is provided on the connecting rod crank bearing according to known gas engine practice. The upper end of the connecting rod 14 has a liner or bushing 35 for receiving the wrist pin 36, which wrist pin is preferably gripped by the piston, being held therein by a cotter pin or the like, so that relative bearing motion between the pin 36 and the liner 35 occurs. Lubrication for this bearing is pro vided by an oil duct 37 extending through the V upper end of the connecting rod and through the liner 35.

Piston construction working or displacement member, the upper part or head portion 40. which performs the actual service of acting as a moving wall for the working chamber 42, has substantially. no guiding function, whereas the lower portion 39 has substantially no displacement function- In fact, the portion 39 does not enter the working chamber 42. The head portion 40, which really-becomes the and 30, which end plates are bolted by means of l working piston or plunger, comprises a circular disc having the frustro-conical dome 43 adapted to enter the discharge passageway 44 for minimizing the clearance. The passageway 44 is formed centrally of the head 45 of the working cylinder 46. The bottom surface of the head 45 is carefully machined, as is the discharge passageway 44, and the cylinder head 40 and itsboss 43 are likewise carefully machined, and the throw of the crank is such that the head 40 approaches the cylinder head 45 almost to actual contact in order to minimize the loss in volumetric efliciency which any clearance at the end of the stroke entails.

The working piston or head 40 is joined to the guiding portion 39 through a rigid crossed web connection 48, which supports the head 40 substantially out of contact with the walls of the cylinder 46, the guiding action being secured mainly by the lower portion 39, and to some extent, if desired, by the oil wiper or oil distributor 47, which comprises a circular disc or wall, cast integral with webs 48, 49, joining the head portion 40 and with the lower portion 39. The disc 47 has, in the present. air cooled compressor, which is of a capacity of 3.13 cubic feet per minute free air displacement, at 1600 to 1700 R. P. M., with two inch bore and one inch stroke, a clearance of approximately .015 inch.

.The lower surface of the disc 47 is dished in at the edges in order to provide a relatively sharp circular edge tending to scrape inwardly and to carry downwardly any excess of lubricant which may lodge upon'the inner wall of the guiding cylinder 2. The disc 47 is joined to the head or piston 40 by two thin Webs crossing each other at right angles forming a light but rigid connection 48 between these parts. The skirt or bottom portion of the piston structure 38 is connected to the disc 47 by four webs 49 which may be considered as continuations of the webs 48. The webs 49 are interrupted at the center in order to provide clearance space at 50 for the upper end of the connecting rod 14. This structure is shown more clearly in the section of Figure 3.

The head or working piston member 40 has a relatively thin central portion and'at the margins the head is thicker in order to provide for the location of a piston ring groove 52. The groove 52 receives the piston ring 53 which is preferably a standard concentric ring having a step joint or other suitable tight connection between the ends thereof. The ring 53 is narrower than the groove 52 by an amount of approximately fifteen to twenty thousandths of an inch in this particular size of compressor. The difference in width may be raised with the bore and stroke. The groove 52 is of a depth great enough to provide a clearance 54 back of the ring 53 as shown on an enlarged scale in Figures 4 and 5. This clearance is indicated at 54 in Figures 4 and 5 and it serves the dual function of clearance for the ring 53 and also as an inlet passageway for the working chamber 42, as will be described more in detail later.

The upper and lower surfaces of the groove are flat, that is, these surfaces are planes lying at right angles to the axis of the'piston 40, so that they are parallel to each other. Likewise, the upper and lower surfaces of the ring 53 are parallel to each other and adapted to fit fiat against the upper and lower end surfaces of the groove 52 and-to form airtight contacts therewith.

The flanges which define the end walls of the groove 52, or which are defined by the groove, are cylindrical and fit within the cylinder 46, namely,

with a minimum clearance for the upper flange 55 and with a clearance of approximately fifteen to twenty thousandths of an inch for the lower flange 56. The reason for the greater clearance of the lower flange is to provide space between said flange and the cylinder wall to permit the entry of air into the working chamber 42 on the intake stroke of the compressor. That is to say, the space between the lower flange 56 and the cylinder wall 46 is a part of the intake passageway of the compressor. This does not need to be uniform all the way around. There might be shallow grooves across the end of the flange 56 instead of a uniform clearance.

A series of holes 57 are drilled in the upper surface of the head 40 in the flange 55, so as to intersect and communicate with the clearance 54 between the ring 53 and the groove 52. The ring 52 makes a tight fit with the cylinder 46. This fit is a peripheral, or cylindrical fit. The ring 53 also makes a tight fit with the flange 56 by pressing against the same in an axial direction and making a flat, or planar fit therewith. The ring 53 has sufficient friction with the walls of the cylinder 46 to cause it to tend to remain in any 10!) position in which it is placed in the cylinder bore, said ring fitting in the groove so freely that the piston tends to move with respect to the ring upon each reversal of motion of the piston. The piston and ring thus have lost motion between 105 them to the extent of fifteen or twenty thousandths of an inch in the particular embodiment herein shown. This, obviously, may be greater or less, as may be desired.

Compression cylinder The compression cylinder 46 is functionally disassociated from the guiding cylinder 2, although it is of the same diameter and structurally is rigidly joined to thesame. The structural connection is made as follows: Adjacent the upper end of the guiding cylinder 2 I provide a radially extending flange 59, having at its outer end a cylindrical axiallyextending flange 60. The upper end of the flange 60 is faced off flat and the inner peripheral surface is machined for the purpose of making a close piloting fit with a flange 62 formed on the lower end of thecompression cylinder 46. The flange 62 has a series of bosses 63, preferably four in number, drilled and threaded to receive the cap screws 64 for clamping the flanges 59 and 62 together. These bosses 63 and the outer periphery of the flange 62 are carefully machined to fit the upper end of the cylindrical flange 60. 46 and 2 are thereby piloted accurately into alignment with each other. The cylindrical flange 60 is at one side provided 'with a threaded pipe socket 65, providing communication between the atmosphere outside and the intake chamber 66, confined within flange 60 and surrounding the upper end of the guiding cylinder 2 and disposed between the two flanges 69 and 62. A suitable dust separator or filter may be interposed between the intake chamber 66 and outside atmosphere, particularly where the compressor is employed for automotive work.

A series of air-cooled fins or vanes 67 are cast integral with cylinder 46 and with the flange 62. These fins 6'7 extend from the boss 102 at the upper end of the discharge check valve chamber, which is disposed in the upper end of the cylinder casting, above the compression chamber 42, along the outer walls down to the flange 62.

The discharge check valve chamber 68 com- '150 The two cylinders 130 municates through a cored passageway 69 indicated by the dotted lines in Figure 1 with the outside, and this cored passageway is preferably provided at its outer end with a threaded pipe socket for connecting the delivery pipe from the chamber 68 to the receiver or other pneumatic connection. The boss 102 at the upper end of the cylinder casting is provided with an axially cored opening which is machined and threaded to receive the recessed plug 70, within which is seated the discharge check valve helical spring 72 for holding the discharge check valve 73 to its seat.

The inner bottom wall of the chamber 68 provides an axially extending annular flange 74 for retaining the discharge check valve 73 over its seat 71. a

The valve 73 is a thin .disc of metal having a series of integral arms extending radially beyond the edge of the seat 71 into proximity to the flange 74, these arms holding the valve in place in the cage which is formed by the flange 74 and the sleeve extension 104 of the plug 70, but permitting air which has passed the seat 71 of the valve 73 to pass freely into the discharge check valve chamber 68.

The recessed plug has its lower end reduced to form a hollow neck in the shape of a thin cylinder extending within the confines of cylindrical flange 74 and limiting the liit of said valve 73, at the same time forming a suitable guide for the discharge check valve spring 72.

The lift of the valve 73 is relatively small, but due to the substantial diameter the gas compressed in the compression chamber 42 finds ample port area between the compressor cylinder and the chamber 68. A valve 01 large area is not desirable because of its weight and inertia, the difficulty of keeping it tight, and the excessive pressure which it then sustains.

While the specific form of valve structure here described is highly advantageous I do not intend to limitthe invention in respect to that feature. It is to be noted, however, that the same general type of discharge valve construction is shown in the modifications later illustrated.

Operation flange 55. The ring 53 having suflicient friction to drag along the cylinder walls will be held .by said friction of motion against the flange 55 during the downward stroke. Now assume that the crank 16 is turned and the piston structure begins to rise. The ring 53 stands still, temporarily, but the piston rises, bringing the lower flange 56 against the ring 53 and, as soon as said lost motion--that is, the minute space between the ring and the end wall of the groove-has been taken up, the ring 53 iscompelled to follow the upward motion of the piston. Thus the passage which was previously wide open is completely closed ofi in an exceedingly small part of the angular cycle of the crankshaft.

The ring 53, bearing against the lower flange 56 and simultaneously bearing against the inside of the cylinder wall 46, forms a fluid tight connection between the working piston 40 and the cylinder 46. The ring is held against said'bottom end wall of the groove by two forces, first, the triotional resistance of the ring sliding along the cylinder walls 46 and second, by the downward or outward pressure of the air compressed in the working chamber 42 by the upward stroke of the piston. In the present instance, since compressed air is admitted back of the ring 53, it tends to expand outwardly against the cylinder walls 46, as well as to be held downwardly against the flange 56, thereby securing an excellent seal between the piston and cylinder wall. So far as I know, this is broadly new.

As the piston travels upwardly the compressed gas is discharged past the valve 73 into the chamber 68 until the stroke is completed, whereupon the check valve 73 closes. The piston then starts on its downward travel. Whereas, on the upward stroke the position of the ring 53 with respect to its groove was as shown in Figure 4, as soon as the piston starts downward and moves a distance equal to the clearance between the ring and the end walls of the groove, the position of the parts relative to each other will then be as indicated in Figure 5. That is to say, the ring 53 will then engage the upper end wall of the groove 54, that is, against the flange 55, and will be drawn downwardly. In fact, the instant thatithe piston begins to move downwardly, the ring 53 leaves its lower seat, which is, in fact, the valve seat, and communication is thereupon opened between theworking chamber 42 and the intake chamber 56, by a passageway of ample size to permit the flow or air into the working chamber 42 to occur freely. I

The space radially between the flange 56 and 119 the cylinder wall 46, while small in radial dimension, is relatively large in circumference and therefore permits of a relatively large total intake area to be secured. The intake passageway comprises the radial clearance 77 between the 11 flange 56 of the piston and the cylinder wall, the clearance 78 between the ring 53 in its upper position and the lower end wall of the groove 52, the clearance space 5% between the ring 53 and the bottom of the groove 52 and the drilled openings 57. The valve controlling this passageway is the packing ring53, and it seats against the lower end wall oi the groove 52 to close oft said intake passageway.

When the compressor is operated at high speed the inertia of the ring acts to help the valve action, rather than to hinder it. Consider, for example, that the piston'is moving inward on its compression stroke-that 'is, toward the cylinder head 45'and the stroke is being completed. The tendency of the inertia of the ring is to throw it ahead with respect to the piston 46. So long as the pressure of the gas upon the ring 53 exceeds the inertia of the ring, the ring will not tend to leave. the valve seat. However, the tendency is there and operates in the right direction. Likewise, when the piston moves downward to the bottom oi. its suction stroke, the tendency is to throw the ring 53 downwardly against its seat, tending thereby to close the valve more quickly, so that the initial motion of the piston 40 will not be lost. This inertia tendency of the ring is relatively inconsequential in the size I have illustrated but it may, under certain circumstances, be importan and I am calling attention to the same.

The clearance introduced by these minute inintake passageway slightly by reducing the width of the ring 53, butthe ring 53 should have suf-' tains the ring and the groove clear and in primev operating condition.

I have described above the pneumatic function of the packing ring as a suitable intake valve. I shall now call attention to the mode of lubrication of the compressor.

Lubrication of the compressor 39 of the piston are copiously lubricated by splash lubrication from the crankcase. The piston structure 38 is so proportioned that the piston member or head 40, which is the working piston for the working cylinder 42, travels solely with-- in said working chamber. Likewise, the guiding portion 39 of the piston structure operates solely within the guiding cylinder 2. The wiper, or lubricant distributor .47, works in both cylinders, namely, the cylinder 2 and the cylinder 46. While its chief function is to prevent the escape of lubricant from the crankcase by forming a seal over the guiding structure 39, it performs, also,

the equally important function of transferring a minute quantity of lubricant from the guiding cylinder 2 to the working cylinder 46.

One of the greatest difliculties in air compression is with lubrication. The ordinary trunk piston of an air compressor must be lubricated sufflciently well to withstand the mechanical thrust and wear to which it is subjectedas a machine element, independent of its pneumatic function. In the present construction I have separated the two functions, namely, the mechanical function and the pneumatic function, since the upper or working piston 40 has little or no guiding function in the cylinder46 and the portion 39 has substantially no pneumatic function. It is, however, desirable to reduce the ring friction, that is, the friction between the ring 53 and the walls of the cylinder 46, and on that account it is desirable to provide a small amount of lubrication in the working cylinder.

About all the oil that is necessary in the working cylinder of this compressor is the equivalent of one or two drops an hour for lubricating the.

ring 53. Anything more than that is unnecessary and, in-faot, detrimental, since it will be passed into the discharged compressed air. By holding the lubrication in the working compressor cylinder to a minimum, many advantages follow. First, the inlet passageway remains free of .oil and the ring does not become gummed with carbonized oil in case of excessive temperature. Likewise, the oil does not accumulate on the discharge check valve and carbonize and cause the valve to leak. It also minimizes any danger of any possible explosion due to oil in the inter-cooler in the case of a compound compressor. There are numerous advantages in sparse lubrication.

The wiper 47 tends to scrape ofl and throw down any excess oil on the guiding cylinder walls Thermal separation It is to be observed that the compressing functionand the mechanical guiding function occur in parts which are-thermally separated. The upper cylinder is separated from the lower cylinder thermally since the connection is in a roundabout way and the heat of the compressing action isnot transmitted to the guiding cylinder except through a circuitous path which has ample opportunity to dissipate the heat before it reaches the guiding cylinder 2. The same thing is true of the two parts of the piston structure. The compressing piston 40 is separated from the guiding piston 39 by a rigid'connection comprising relatively long, thin walls which are freely The guiding cylinder 2 and the lower portion in contact with the air in the intake chamber 66. The head 40 is composed of a relatively thin contact with the air which is constantly changed,

due to the proximity of the intake passageway with the same, particularly at the beginning of the intake stroke. Thus the hottest air, namely, that immediately below the piston head 40, will be drawn into the cylinder at the beginning of the stroke and colder air will be drawn in to-' wards the latter part of the stroke, with the result that there is a certain stratification and a consequent selective expulsion of the highly heated air at the beginning of the stroke, followed by the expulsion of the cooler air which is introduced into the working chamber atthe last part of the intake stroke.

Due to this thermal separation of the parts tions where the compressors of the prior art would fail.

It is not intended to limit the present invention to a small size compressor as the principles of the invention are applicable in all sizes. However, in even the relatively small size which I have herein illustrated remarkably high efficiencies are secured and this is a performance which the prior art has not attained.

Modifications of the inlet valve construction I do not intend to limit the invention to the specific form of inlet valve construction shown in Figures 1 to 5. In Figures 9 to 13 I show a series of suggested modifications. These modifications are not shown by way of limitation, but of explanation. They do not exhaust byany means the variations which are possible within the principles taught herein.

In Figure 9 the ring 53 is provided with an upwardly extending flange 80 which is engaged by the upper flange 55 of the piston 40 on the downward stroke, the main body of the ring 53 being held away from the drilled passageways 5? during the intake stroke and the air entering by way of drilled passageways 82 under the ring 53, through the clearance between the bottom of the groove and the ring 54 and the space between the body of the ring 53 and the flange 55, and up through the drilled passageways 57. The drilled passageways 5'7 and 82 may be aligned, that is, formed by a through drilling.

The action is the same' as described in connection with Figures 1 to 5.

In Figure 10 I have shown the ring 83 as provided with a series of drilled passageways 84 which are obstructed by the lower flange 56 on the compression stroke, but which are not obstructed by the relatively short flange 55 on the suction stroke. The inlet passageway in that case comprises the clearance between the flange 56 and the cylinder wall 46, the drilled passageways 84 and the clearance between the flange 55 and the cylinder wall 46. The operation is substantially the same as that described in connection with Figures 1 to 5.

In Figure 11 the ring 83 is provided with a series of diagonal drilled passageways 85, the lower ends of which passageways are obstructed by the lower flange 56 and the upper ends of such passageways '85 being not obstructed by the upper flange 55. The operation of this construction is substantially as described in connection with Figures 1 to 5 and paralleling the construction shown in Figure 10.

In Figure 12 the ring 86 is confined loosely in the ring groove between the flanges 55 and 56 to permit shifting thereof relative to the piston, and this ring 86 carries a flat, annular valve member 87, which serves to close, on the discharge stroke. the drilled passageways 88, but which does not obstruct at any time the drilled passageways 89 above the same. This modification operates substantially the same as described in connection with Figures 1 to 5, it being noted, however, that the actual valve function is performed by a member moved by the ring 86 instead of combining the two functions of valve andring in the same structure. The ring 86 has a relatively slight lost motion with respect to the valve 87.

In Figure 13 I have illustrated a modified construction in which the ring 90 is not wholly contained within the groove out has a flange 92 which is slotted, or notched, so as to provide, in effect, a series of projections from the ring 90 into a narrow groove 93 formed in the piston 40. The lower flange 56 cooperates with the ring 90 to seal the inlet passageways, that is, the space between the piston 10 and the cylinder wall 46, upon the upward or compression stroke. On the downward, or suction stroke, the projections 92 are caught by the upper end wall of the groove 98 and air passes in between the flange 56 and the Modifications of the compressor In Figure 6 I have shown a modified form embodying one of my previously patented methods of cooling. In this construction an air receiver, or chamber 95 is mounted outside of the cylinder 46 and held in place by the recessed plug '70. The plug 70 has a flange 96 overhanging the margins 97 of the opening through which the plug is passed, so as to press the chamber 95 onto the seat 98 formed on the huge 82 of the cylinder casting 46. Gaskets are supplied to make tight joints.

The receiver or chamber 95 is preferably a casting provided with a series of external cooling fins or ribs, 99, and internal reinforcing ribs 100, for strengthening the body of the casting and to assist in cooling. The receiver casting 95 has a relatively large chamber which spaces the receiver walls from the cylinder 46.

The boss 102, which forms an extension of the cylinder walls 46, is threaded to receive the threaded portion of the plug '70 and ports such as 103 are provided between the valve chamber 68 and the receiver 95. The lower end of the plug 70 has a thin cylindrical extension 104 which is provided with ports 105 to provide free communication between the chamber 68 and they interior of the hollow plug-70. The plug 70 in this case has a delivery passageway 106 terminating .for any excess pressure is provided. The receiver 95 performs a highly desirable function, that is, the cooling function disclosed and claimed in my prior patents above referred to, namely, Nos. 1,699,941 and 1,714,836. This will be appreciated from the mode of operation, which is as follows:

As the working piston 40 is moved upwardly in the wormng cylinder 42, the check valve 781s raised from its seat 71 and air is discharged around the edges of the check valve over the flange 74 and part of the same passes out through the passageways 105 in the sleeve 104 forming an extension of the plug 70 and part passing into the receiver 95 through the ports 108. The instantaneous rate or delivery by the compressor piston is in excess of the rate of delivery out through the delivery passageway 106, with the result that during a discharge stroke of the compres'sor, air is moving into the receiver 95, while during the suction stroke of the compressor, air is moving from the receiver 95 back through the ports 108, chamber 68, ports 105 and the lower end of neck 104, which was closed off by rise of the check valve during the discharge stroke, and out through the discharge passageway 106. Due to the large cooling area of the fins and exterior surfaceoi the receiver 95, and due, also, to the interior fins 100, a relatively rapid heat inter- -change from the compressed air to the surrounding atmosphere occurs. This is sufficient to limit the temperature rise to a safe value at all times. The size of the'chambe r 95 may, of course, be varied to meet individual requirements and to provide a suflicient cooling surface to limit the temperature rise, but as above indicated, for apparatus which,- while in use, continuously uses the full delivery of the compressor, only sufficient capacity is required to secure the cooling function and to serve'as a cushion when the spray gun, or the like, is shut off, to keep the'pressure from being flashed to 'too high value.

The other parts of the compressor are substantially identical with those shown inFigures 1 to 5 and reference may be had to the previous de-' scription for an explanation of the same.

Water jacketed compressor form the receiver in the embodiment of Figure 6.

The casting or chamber 110 differs from the chamber 95 only in the provision of a pipe socket 112 from which the water is conducted. The passageway 108, which has a pipe socket 109, in this case serves as the inlet for the cooling water,

the discharge of which occurs through the outlet 112. The cylinder casting 46 in this case has a closed, discharge check valve chamber 68, as in the embodiment of Figure 1. The delivery of air, however, is through the plug 70, as in the embodiment of Figure 6. The air is discharged past the check valve 73 into the chamber 68 and then it passes through the ports 105 into the bore of the plug 70 and out through the delivery passageway 106 to, the delivery pipe. It will be observed that the lower end of the plug 70 is always so closely adjacent the discharge check valve 73 that the said valve 73 will be pressed against the lower end of the sleeve 104 upon the delivery stroke. Therefore, when air is being discharged from the compression chamber by the piston 40 the lower end of the sleeve 104 is closed off by the valve itself and the discharged air is comto travel out into the chamber 68 and to come into contact with the walls of the chamber 8, which are subjected to cooling, and the air whichis delivered during the delivery stroke must pass through the ports 105. As soon as the check valve 73 drops back to its seat, the lower end of the sleeve 104 is opened and to whatever extent the pressure inthechamber 68 is higher than in the delivery pipe or receiver proper, the continuation of flow of air tends to cool the check valve itself and its immediately adjacent metal parts, so that no pockets of hot air are permitted to accumulate. In this manner cooling is carried out as in the embodiment of Figure 7 and as first,

disclosed in my aforesaid patents. In the present structure the discharge check valve is smaller and is water cooled. In Figure 6 it is larger and is air cooled.

4 Lubrication control greater width than the width of the ring, to provide a clearance 117 between the ring and the end walls of'the groove.' The groove communicates with a passageway 118 leading to the central open space 119 below the wall 120 of said guiding portion 39101 the piston structure. The ring 115 is a standard concentric piston ring having the usual step joint like the, ring 53 and it operates as a check valve, like the ring 53. Due to the splash offthe oil thrower, or dipper 33, the walls of the guiding cylinder 2 are copiously lubricated. As the piston rises from the position shown in Figure 7 to make the compression stroke, the natural tendency for the ring 115 is to lag, because of its frictional engagement with the walls of theguiding cylinder 2, behind the motion of guiding cylinder 2 and the same is then drawn constructed, for two reasons.

the piston. The result is that-the ring 115 chgages the lower end wall of the groove, leaving the clearance 117 between the upper end wall of the groove and the ring 115. This provides, therefore, a passageway as follows, namely, from the space between the piston head 40 and the wall 120, through the clearance between the wall 120 and the cylinder walls of the guiding cylinder 2, clearance 117 between the ring and the groove and the radial clearance between the bottom of the groove and the back of the ring 115, passage-' way 118 to the open space 119, and thereby to the crank chamber.

As the piston rises there is a tendency to-form a vacuum in the crank chamber and this I pref erably arrange to augment by a tight crank chamber and the use of a check valve 122. As the ring 115 moves upwardly in the guiding cylinder 2 it tends to scrape lubricant off the walls of the through the aforementioned passageway into the crank chamber. The scraping from the walls is mechanical and the removal of the excess lubricant thus scraped is pneumatic.

. When the piston has reached the top of its stroke the ring 115 seizes the walls with whatever 'friction it has, and as the piston descends the ring lags behind and engages the upper end wall of the groove 116, closing off communication between the bottom of the wall 120 and the top thereof. Any oil which is now scraped from the walls by the ring 115 cannot be driven upwardly, as is the tendency in compressors as heretofore First, the ring 115 prevents discharge past the same by such pneumatic pressure as is created in the crank chamber and second, I preferably make provision for releasing such pressure as might be generated in the crank chamber through the provision of the automatic check valve 122 aforementioned.

It is to be observed that atmospheric pressure prevails in the space between the head 40 and the intervening head 120, so that the formation of a reducedarea of pressure within the crank case does not affect the pneumatic action of the working head or piston 40 in its working cylinder 46. While this is the desirable and preferred construction I wish it to be understood that this phase of the invention. is applicable to compressors where the intake port extends through the walls of the cylinder itself and to a construction which does not interpose atmospheric pressure between the guiding portion of the cylinder and the working, or pneumatic head of the piston.

Lubrication ofthe working cylinder 46 in this case is effected by a. series of projections 123 on the webs 48. These projections contact alternately with both cylinders and serve to carry across the gap between the cylinders sufficient lubrication to keep the ring 53 in the cylinder 46 sumciently lubricated for satisfactory operation. The crank case in this construction is rendered substantially airtight by suitable packing 124 along the crank shaft 16. Obviously, any suitable manner of making a comparatively tight joint or a completely tight pneumatic joint may be provided. The end plate 20 in this case is provided with an extension 125 through which there is formed a passageway 126 and in the upper end of which there is formed a suitable valve cage for the check valve 122,. The housing 127 has a valve seat 128 surrounded by a relief groove and by the cylindrical walls of the chamber 127 for guiding the flat check valve 129, which isprowithin the cylindrical walls of the chamber 127. A ported plug 130, having a discharge passageway 132 and a discharge check valve spring chamber 133 for receiving the spring 134 is threaded into the open end of the housing 127. The lower end of the spring 134 bears upon the valve 129 and holds it lightly to seat. The lower end of the plug 130 has a flanged extension which is notched, as indicated at 135, to permit .the discharged air to pass freely out through the ported plug 130.

It will now be seen that as the piston descends there is a tendency to compress the air in the crank case and to force the same out past the valve 129. At that time the projections 123. which have a very slight clearance, possibly fif! teen thousandths of an inch on one side, in the bore of the guiding cylinder 2, descend into the guiding cylinder and contact with the oil on the walls of the cylinder. As the piston thereafter rises, the ring 115, engaging the lower end of its groove, opens a passageway for permitting air and the oil which is scraped from the walls of the guiding cylinder 2, to be drawn down into the crank chamber as the piston rises. At the same time,- the projections 123 of the piston 40 transfer a film of oil to the walls of the compression cylinder 46, providing sufficient lubrication therefor.

It is, of course, possible to employ usefully the air which is compressed in the crank chamber that is to say, the compressor may be made double acting if desiredbut in the specific construction illustrated, that is not the intention. The passage of air above described through the guiding cylinder, piston and crank case serves to ventilate and cool the same.

As the guiding piston and cylinder, separate from but aligned and connected with the compressing piston and cylinder, is new, I intend to cover this feature broadly, independently of the location and character of the intake valve or the discharge valve. For example, no intake valve at all need be provided if the piston 40 has an overrun intake port, or if it is pulled clear of the cylinder 46 on the end of the suction stroke. Conceivably, also, a cup leather or its equivalent might be employed instead of the packing ring and the air introduced by contraction of the same. As numerous features are new independently of each other I do not intend to limit the claims to nonessential or optional features.

I claim:-

1. The method of cooling a compressor which comprises, moving air along the pistonand in contact therewith' into the crank case on ,one stroke of the piston and expelling the air from the crank case along a path out of contact with the piston on the other stroke thereof.

2. In combination, a working cylinder, a guiding cylinder in axial alinement therewith, there being an air inlet between said cylinders, a piston comprising a head member fitting in the working cylinder, and a guide member fitting in the guiding cylinder, said piston members having a connection between them and an oil wiper carried by said connection and adapted to transfer oil from the guiding cylinder to the working cylinder.

3. In combination, a working cylinder open at its lower end and closed at its upper end, a guiding cylinder open at its upper end, said cylinders being of substantially the same diameter and being supported in axial alinement, a rigid piston a member comprising a piston head workingin the working cylinder and a guiding portion whereby ;for the admission of air to the cylinder, said the entire memberis guided in the guiding cylinder, said member having a lubrication control portion for carrying lubricant from the walls of the guiding cylinder to the working cylinder, and means for reciprocating said member.

4. In combination, a compressor cylinder, a piston fitting loosely therein to provide a.,clearance, a guide for guiding the piston independently of the cylinder, a wrist pin disposed in the guide a piston ring for the piston having slidable but fluid tight engagement with the inner wall of the cylinder, said piston having a ring groove for receiving the ring, the ring having endwise play in the groove, there being an intake passageway passageway including the clearance between said piston and cylinder and including the clearance between the ring and the end wall of the groove and being adapted to be closed off by initial movement of the piston in an outward direction.

5. In combination, a pumping cylinder having an integral discharge check valve chamber provided with a check valve therein, a radially extending mounting flange being formed about the lower open end of the pumping cylinder, a frame including a crank case and guiding cylinder, said guiding cylinder having a cylindrical guiding flange surrounding the guiding cylinder and engaging the radially extending mounting flange of the pumping cylinder and cooling means .extending from said mounting flange to the upper end of said valve chamber.

6. In combination, a crank case, a guide cylinder mounted thereupon, the upper end of the cylinder being open, an open toppedair trunk surrounding the upper end of the cylinder, a compression cylinder having a flange at its lower end and being mounted by engagement with the air trunk only, a crank for the crank case, a crosshead guided in the first cylinder, a piston working in the second cylinder,- said piston be-- ing rigidly mounted on said crosshead and being guided thereby, out of contact with the second cylinder, a ring between the said piston and its cylinder and a connecting rod connecting the crank and the crosshead.

'7. In combination, a crank case, a guide cylinder mounted thereupon, the upper end of the cylinder being open, an open topped air trunk surrounding the upper end of the cylinder, a compression cylinder having a flange at its lower end mounted on the air trunk, a crank for the crank case, a crosshead guided in the first cylinder, a piston working in the second cylinder, said piston being rigidly mounted on said crosshead and being guided thereby, and a connecting rod connecting the crank and the crosshead, the two cylinders being of substantially the same diameter, and means carried by the crosshead and contacting alternately with the two cylinders for transferring lubricant from the guide cylinder to the compressor cylinder.

8. In combination, a crank case. a guide cylinder mounted thereupon, the upper end of the cylinder being open, an open topped air trunk surrounding the upper end of the cylinder, a compression cylinder having a flange at its lower end mounted on the air trunk, a crank for the crank case, a crosshead guided in the first cylin- 1 5 der, a piston working in the second cylinder, said piston being rigidly mounted on said crosshead and being guided thereby, and a connecting rod connecting the crank and the crosshead, said compressor cylnder being of a length substantialLv equal to the throw of the crank plus the groove providing the length of the piston, and means between the 'piston and crosshead for transferring oil by contact from the guide cylinder to the compressor cylinder.

9. In combination, a crank case, a crank shaft therein, a guide rigid with the crank case, a cylinder beyond the guide, the cylinder and guide being connected by a hollow enlargement about the adjacent ends of the guide and cylinder forming internally an air intake admission chamber and providing a circuitous path only for heat conduction between the guide and cylinder, a crosshead in the guide, and a piston in the cylinder connected to the crosshead.

10. In combination, a crank case, a crank shaft therein, a guide rigid with the crank case, a cylinder beyond the guide, the cylinder and guide being connected by a hollow enlargement about the adjacent ends of the guide and cylinder forming internally an admission chamber and providing a circuitous path for heat conduction between the guide and cylinder, a crosshead in the guide, a piston in the cylinder connected to the crosshead, and means between the piston and the crosshead for contacting alternately with the guide and with the cylinder for transferring oil from the guide to the cylinder.

11. In combination, a crank case, a crank shaft therein, a guide rigid with the crank case, a cylinder beyond the guide, the cylinder and guide being connected by a hollow enlargement about the adjacent ends of the guide and cylinder forming internally an admission chamber and providing a circuitous path for heat conduction between the guide and cylinder, a crosshead in the guide, and a piston in the cylinder connected to the crosshead, intake and outlet valve means for the crank case for passing ventilating air through the crank case.

12. In combination, a crank case, a crank shaft therein, a guide rigid with the crank case, a cylinder beyond the guide, the cylinder and guide being connected by a hollow enlargement about the adjacent ends of the guide and cylinder forming internally an admission chamber and providing a circuitous path for heat conduction between the guide and cylinder, a crosshead in the guide, and a piston in the cylinder connected to the crosshead, a ring carried by the crosshead, said crosshead having an intake passageway from the admission chamber to the crank case, said ring serving as an oil scraping rin and as a valve for said passageway.

13. The combination with a cylinder having a discharge valve of a piston comprising a head having a relatively thin wall and a short cylindrical skirt, said skirt having a peripheral ring groove with planar radially extending walls, and a ring of less width than the groove disposed in said groove and cooperating with the cylinder, clearance back of the ring communicating with the clearance between the ring and theend walls of the groove and open communication .being provided between the clearance back of the ring and the top of the piston, said piston being of a diameter substantially less than that of the cylinder to provide a clearance between them, said clearances providing an intake passageway, and means for guiding the piston in the cylinder out of contact with the cylinder walls.

14. In combination, a cylinder, a piston therefor having a head and a relatively short skirt, said skirt having a ring groove, a ring narrower than the groove disposed in the groove and having clearance at its ends with'the end walls of the groove and at its back with the bottom of the groove, the portion of the skirt below the ring providing a clearance with the cylinder forming a part of an intake passageway which is controlled by the ring, said ring forming the only fluid sealing joint between the piston and the cylinder.

15. In'combination, a cylinder having a discharge passageway, a piston for the cylinder, the piston and cylinder having a clearance between themproviding an intake passageway, a metallic piston ring for the piston, said intake passageway being controlled by the ring acting as a valve, and means for guiding the piston in the cylinder independently .of the cylinder walls.

16. In, combination, a cylinder having a discharge passageway, a piston for the cylinder, there being an annular clearance between piston and cylinder forming an intake passageway, a piston ring for the piston, said intake passageway being controlled by the ring acting as a valve, means for guiding the piston concentrically in the cylinder independently of the walls of the cylinder and substantially out of contact therewith, and means for lubricating the bearing of the piston ring in the cylinder.

17. In combination, a cylinder having a discharge passageway, a piston for the cylinder, a ring groove in the piston providing an intake passageway, a piston ring fitting loosely in the groove and fitting tightly the cylinder walls, there being a clearance between piston and cylinder forming an intake passageway, and means independent of the cylinder for guiding the piston in the cylinder.

18. In combination, a working cylinder, a guiding cylinder in axial alinement but out of direct thermal contact therewith, there being a fluid inlet between said cylinders, a piston member comprising a head member fitting in the working cylinder and a guide member fitting in the guiding cylinder, said head member and said guiding member being spaced apart by a distance substantially equal to the stroke of the piston member, said head member and guide member having a rigid connection between them and a wiper between the guide and piston ,for carrying lubricant from the guiding cylinder to the working cylinder.

19. In combination, a compressor cylinder, a piston adapted for reciprocation in the cylinder, there being clearance between the pistonand cylinder great enough to avoid substantial contact between them and to provide an intake passageway for air into the cylinder, means out of the said radial clearance of ring and groove and the space above the piston.

20. An air compressor comprising a compressing cylinder, a tubular guide, said cylinder and guide having their adjacent ends separated to provide an air admission passageway between them, a' crank case connected to the tubular guide, a crosshead in the guide, a piston in the cylinder rigidly connected to the crosshead, an

- inlet check valve carried by the piston opening into the cylinder, an inlet check valve carried by the crosshead and opening into the crank case, a crank in the crank case, a connection between the crank and-the crosshead, a discharge check valve from the crank case and a discharge check valve from the cylinder.

21. An air compressor comprising a compressing cylinder, a tubular guide, said cylinder and guide having their adjacent ends separated to provide an air admission passageway between them, a crank case connected to the tubular guide, a crosshead in the guide, a piston in the cylinder rigidly connected to the crosshead, an inlet check valve carried by the piston opening into the cylinder, an inlet check valve carried by the crosshead and opening into the crank case, a crank in the crank case, a connection between the crank and the crosshead, a discharge check valve from the crank case and a discharge check valve from the cylinder, said inlet valves comprising axially movable ring valves contacting with the guide and with the cylinder respectively, and means between the crosshead and the piston for transferring lubricant from the guide to the cylinder.

22. In combination a crank case, a crank shaft therein, a tubular guide member rigid with the crank case, said guide member having a radially extending-flange, a cylindrical crosshead reciprocable in the guide member, a compressor cylinder member aligned with the guide member and having also a radially extending flange, a cylindrical spacing element disposed between said flanges and defining with said flanges an air intake trunk and spacing the lower end of the cylinder member fromthe upper end of the guide member to form a relatively narrow circumferential inlet passageway communicating with said air intake trunk, said spacing element and flanges keeping the members from direct thermal contact and providing two cylindrical surfaces discontinuous from each other, and a piston in the cylindrical member, said piston being rigidly connected to the crosshead and guided thereby in the cylinder.

23. Incombination a crank case, a crank shaft therein, a tubular guide member rigid with the crank case, said guide member having a radially extendingflange, a cylindrical crosshead reciprocable in the guide member, a compressor cylinder member aligned with the guide member and having also a radially extending flange, a cylindrical spacing element disposed between said flanges and deflning with said flanges an'air intake trunk and spacing the lower end of the cylinder member from the upper end of the guide member to form a relatively narrow circumferential inlet passageway communicating with said air intake trunk, said spacing element and flanges keeping the members from direct thermal contact and providing two cylindrical surfaces discontinuous from each other, and a piston in the cylindrical member, said piston being rigidly connected to the crosshead and guided thereby in the cylinder, said piston being of a diameter such as to provide a clearancewith the walls of the cylinder member to form an intake passageway and an axially movable rigid piston ring serving as an intake valve carried by the piston and having substantially fluid tight engagement with the cylinder member. 24. In combination a compressor cylinder, 9. guide cylinder, said cylinders having their ends adjacent to each other and being disposed in axial alinement, a piston in the compressor cylinder, a crosshead in the guiding cylinder guiding the piston in the compressing cylinder, and means holding said cylinders rigidly in alinement but pneumatically and therma ly separated, and the cylindrical working surfaces of the two cylinders being discontinuous.

25.. In combination, a crank case, a crank shaf therein, a guide rigid with the crank case, a cyl inder beyond the guide, the cylinder and guide being connected by a hollow enlargement about the adjacent ends of the guide and cylinder and of a larger diameter than either the guide or the cylinder, said enlargement providing a circuitous path-only for heat conduction between the guide and cylinder, a crosshead in the guide, and a piston reciprocable wholly in said cylinder and 11 operatively connected with said crosshead.

26. A compressor having a cylinder wall, means forming a surface adiacent to but separate from said cylinder wall, means establishing'a fllm of lubricant upon said'surface, and means forming I a carrier surface movable into contact with both said cylinder wall and said adjacent surface to transfer a part of said lubricant fllm from said adjacent surface to the cylinder wall.

27. A pneumatic cylinder having a cylinder wall and a reciprocable piston therein, means forming a guide surface adjacent to but separate from said cylinder wall, means establishing a fllm of lubricant upon said surface, means form- 1 ing atransfer surface movable into contact with both said cylinder wall and said adjacent. surface to transfer a part ,of said lubricant fllm from said adjacent surface to the cylinder wall, and means for moving said transfer surface from the guide surface to said cylinder wall and vice versa.

BURTON S. AIRMAN. 

